1. Field of the invention
The present invention relates to sensing systems, and in particular, to position sensors for providing signals indicative of the position of a moving member relative to some fixed datum. By appropriate processing of the position signals, further signals indicative of the speed of movement of the moving member relative to this datum may also be derived. Sensors of this kind are applicable to a multiplicity of uses. The invention is particularly directed to a linear embodiment of sensor especially suited to establishing the location of a moving member. The invention is further directed to the provision of a sensing system for monitoring the location of vehicles moving along a predetermined path, as well as the provision of systems for guiding moving vehicles and constraining them to follow such a predetermined path.
2. Description of the prior art
Position and speed sensors of the foregoing kind form the subject of co-pending U.S. patent application Ser. No. 789,147, now allowed. According to this Application, there is provided a sensor comprising a drive or exciting winding for establishing a forward or drive field, at least one secondary or sense winding in which a voltage may be induced in the presence of said forward or drive field, and at least one conductive screen within which eddy currents are generated in the presence of said forward or drive field to establish a counter-field opposing said forward or drive field, said at least one conductive screen and said at least one secondary or sense winding being displaceable relative to one another within said forward or drive field so that said at least one secondary or sense winding may be shaded by said at least one conductive screen to a varying extent to thereby vary the voltage induced in said at least one secondary or sense winding, the relative displacement of said at least one conductive screen and said at least one secondary or sense winding being limited to substantially a single direction of displacement, said drive or exciting winding being configured so that in the absence of said at least one conductive screen said forward or drive field is substantially even over said at least one secondary or sense winding in said single direction of relative displacement of said at least one conductive screen and said at least one secondary or sense winding, said at least one secondary or sense winding being a two-terminal winding, and said at least one conductive screen having a surface region which is substantially parallel to a notional surface defined by said at least one secondary or sense winding.
Said surface region of said at least one conductive screen may be substantially planar and said at least one secondary or sense winding may be a substantially flat winding defining a plane substantially parallel to said surface region, while said at least one screen and said at least one secondary or sense winding are then suitably relatively linearly displaceable.
In an advantageous construction of sensor according to said co-pending Application, there is a further secondary or sense winding the progressive shading of which during said relative displacement of said at least one conductive screen and said at least one secondary or sense winding proceeds in a manner substantially identical with the progressive shading of said at least one secondary or sense winding during said relative displacement, said further secondary or sense winding being disposed relative to said at least one secondary or sense winding so that the progressive shading of said further secondary or sense winding during said relative displacement is spaced apart from that of said at least one secondary or sense winding, the voltage variations in each said secondary or sense winding during said progressive shading preferably following a cyclic pattern and said further secondary or sense winding being disposed relative to said at least one secondary or sense winding so that said voltage variations are in phase quadrature.
In a favoured winding arrangement, said at least one secondary or sense winding has first and second coils, said coils being connected so that in the presence of said forward or drive field the voltage induced in the second coil in the absence of said at least one conductive screen is substantially equal in magnitude but opposite in polarity to the voltage induced in the first coil, said at least one secondary or sense winding preferably having a plurality of coils extending in said single direction of relative displacement and each successive coil in said single direction of relative displacement being wound in the opposite electrical sense to each adjacent coil.
In an especially favoured arrangement, said at least one secondary or sense winding has at least one coil having a pitch or extent in said single direction of relative displacement and said at least one conductive screen has a pitch or extent in said single direction of relative displacement which is substantially equal to the pitch or extent of said at least one coil, said at least one conductive screen having a dimension in a direction at right angles to said single direction of relative displacement which is substantially constant over said pitch or extent of said at least one conductive screen and said at least one secondary or sense winding having a dimension in a direction at right angles to said single direction of relative displacement which is substantially constant over said pitch or extent of said at least one coil, said screen dimension in said direction at right angles to said single direction of relative displacement being substantially equal to the maximum dimension of said at least one secondary or sense winding in said direction at right angles to said direction of relative displacement.
Alternatively, said at least one secondary or sense winding has at least one coil having a pitch or extent in said single direction of relative displacement and said at least one conductive screen has a pitch or extent in said single direction of relative displacement which is substantially equal to the pitch or extent of said at least one coil, said at least one conductive screen having a dimension in a direction at right angles to said single direction of relative displacement, said at least one secondary or sense winding having a dimension in a direction at right angles to said single direction of relative displacement, and at least one of said dimensions varying over the pitch or extent of said at least one conductive screen or the pitch or extent of said at least one coil so that successive incremental net changes in unscreened area of said at least one secondary or sense winding during said relative displacement are governed by a substantially sinusoidal function.
In an advantageous construction, said at least one secondary or sense winding is a printed circuit winding having first and second tracks disposed on opposite sides of a single board, each of said first and second tracks having a plurality of concentric turns, the turns of the first track extending inwardly from the first terminal of said at least one secondary or sense winding to an interconnection with the second track said interconnection passing through said board, and said second track extending outwardly from said interconnection to the second terminal of said at least one secondary or sense winding said first and second tracks being disposed in an aligned back-to-back configuration, and the cross-overs between successive turns of each of said first and second tracks being aligned with each other so that unbalanced electrical effects may be substantially minimized.
In a further aspect, said co-pending Application provides a sensor comprising a drive or exciting winding for establishing a forward or drive field, at least one secondary or sense winding in which a voltage may be induced in the presence of said forward or drive field, and a plurality of conductive screens within which eddy currents are generated in the presence of said forward or drive field to establish a counter-field opposing said forward or drive field, said plurality of conductive screens and said at least one secondary or sense winding being displaceable relative to each other within said forward or drive field so that said at least one secondary or sense winding may be shaded by said plurality of conductive screens to thereby vary the voltage induced in said at least one secondary or sense winding, the relative displacement of said plurality of conductive screens and said at least one secondary or sense winding being limited to substantially a single direction of displacement, said drive or exciting winding being configured so that in the absence of said plurality of conductive screens said forward or drive field is substantially even over said at least one secondary or sense winding in said single direction or relative displacement, said at least one secondary or sense winding being a two-terminal winding, and each of said plurality of conductive screens having a surface region which is substantially parallel to a notional surface defined by said at least one secondary or sense winding.
In yet another aspect, said co-pending Application provides position-measuring apparatus comprising two sensors, each having a drive or exciting winding for establishing a forward or drive field, at least one secondary or sense winding in which a voltage may be induced in the presence of said forward or drive field, and a plurality of conductive screens within which eddy currents are generated in the presence of said forward or drive field to establish a counter-field opposing said forward or drive field said plurality of conductive screens and said at least one secondary or sense winding of each of said sensors being displaceable relative to one another within said forward or drive field so that said at least one secondary or sense winding may be shaded by said plurality of conductive screens to a varying extent to thereby vary the voltage induced in said at least one secondary or sense winding, the relative displacement of said plurality of conductive screens and said at least one secondary or sense winding of each of said sensors being limited to substantially a single direction of displacement said single direction of displacement being the same direction for each of said sensors, said at least one secondary or sense winding of each of said sensors having a plurality of coils extending in said single direction of relative displacement and each successive coil in said single direction of relative displacement being wound in the opposite electrical sense to each adjacent coil and the number of conductive screens of one of said sensors differing from the number of conductive screens of the other of said sensors.
In a still further aspect, said co-pending Application provides a sensor comprising a drive or exciting winding for establishing a forward or drive field, at least two secondary or sense windings in which a voltage may be induced in the presence of said forward or drive field, and at least one conductive screen within which eddy currents are generated in the presence of said forward or drive field to establish a counter-field opposing said forward or drive field, said at least one conductive screen and said at least two secondary or sense windings being displaceable relative to one another within said forward or drive field so that each of said at least two secondary or sense windings may be shaded by said at least one conductive screen to a varying extent to thereby vary the voltage induced in said at least two secondary or sense windings, one of said at least two secondary or sense windings being oriented to provide a varying voltage output substantially indicative of the position of said at least one conductive screen in a first direction of relative displacement of said at least one conductive screen and said at least two secondary or sense windings, and the other of said at least two secondary or sense windings being oriented to provide a varying voltage output substantially indicative of the position of said at least one conductive screen in a second direction of relative displacement of said at least one conductive screen and said at least two secondary or sense windings.
Finally, there is also provided according to said co-pending Application a sensing system comprising a sensor having a drive or exciting winding for establishing a forward or drive field, at least one secondary or sense winding in which a voltage may be induced in the presence of said forward or drive field, and at least one conductive screen within which eddy currents are generated in the presence of said forward or drive field to establish a counter-field opposing said forward or drive field, said at least one conductive screen and said at least one secondary or sense winding being displaceable relative to one another within said forward or drive field so that said at least one secondary or sense winding may be shaded by said at least one conductive screen to a varying extent to thereby vary the voltage induced in said at least one secondary or sense winding, said relative displacement of said at least one conductive screen and said at least one secondary or sense winding being limited to substantially a single direction of displacement, said drive or exciting winding being configured so that in the absence of said at least one conductive screen said forward or drive field is substantially even over said at least one secondary or sense winding in said single direction of relative displacement of said at least one conductive screen and said at least one secondary or sense winding, said at least one secondary or sense winding being a two-terminal winding, and said at least one conductive screen having a surface region which is substantially parallel to a notional surface defined by said at least one secondary or sense winding, means for applying an alternating voltage to said drive or exciting winding, and means for processing the output signal from said at least one secondary or sense winding to provide a signal indicative of the relative disposition of said at least one conductive screen and said at least one secondary or sense winding.
A screened inductance sensor may be regarded, therefore, as a position measurement device in which inductive coupling between two windings is controlled by the position of a passive, conductive screen. Both windings may be stationary with respect to one another and may be fixed in an absolute sense also. Relative displacement takes place between the screen and the sense winding, or, normally in most constructions, relative to both windings. The output of the sensor thus indicates the position of the screen relative to the sense winding, or relative to the two mutually stationary windings.
Position and speed measurement systems based on the screened inductance principle are remarkable for the ease with which a diversity of sensor geometries, covering a wide range of shapes, sizes and accuracy levels can be designed and manufactured. This is a direct result of the inherent simplicity of the basic device and the materials used in its construction.
In a favoured position measuring configuration, a screened inductance sensor system has, therefore, in summary:
(a) a drive winding, PA0 (b) means for energising the drive winding to set up an alternating magnetic drive field, PA0 (c) at least one sense winding to link the drive field, PA0 (d) a screening element for modulating the spatial distribution of the drive field and PA0 (e) means for measuring variations in voltage induced in said at least one sense winding to provide an indication of the relative positions of the screening element and said sense winding.